1. C. H. Edwards, Advanced Calculus of Several Variables, Academic Press, New York, 1973.
2. S. Mac Lane and G. Birkhoff, Algebra, Macmillan, New York, 1967.
3. J. Milnor, Morse Theory, Annals of Mathematics Studies #51, Princeton Univ. Press, Princeton, 1963.
4. J. Milnor, Topology from the differentiable viewpoint, Univ. Press of Virginia, Charlottesville, 1965.
5. M. Morse and S. S. Cairns, Critical Point Theory in Global Analysis and Differential Topology, Academic Press, New York, 1969.